An easy solve today, with the theme clue (16, 20d) readily worked out. The theme answer led me to expect that there would be some other answers meaning "ducks" & that these would all appear in rows - but quite a tour de force for DA to manage every row (apart from the theme answer itself) being comprised of ducks in one meaning or another.

1d IMMUNISE: MM contained within [(c)UISINE]*
2d HECKLE: Heckle & Jeckle are a pair of identical cartoon characters - actually magpies cf. crows according to Wikipedia
3d TSAR: hidden reversed within "drastic". "Overthrow" works as an anagrind but query as reversal indicator
4d PAIN: I think of patisserie as French for a shop that produces cakes & pastries. Query the reference to producing bread (French pain)- better thought of as the traditional function of a boulangerie.
5d FLAMBEAU: (FUME, A LAB)*
6d ERLANG: hidden word. I initially disliked the definition, remembering from a brief period working in the industry that "erlang" is a unit of telco traffic, not "telco traffic". But then we would accept "length" and "metre" etc. as crossword synonyms
9d GOBSTOPPERS: GO, BOPPERS containing ST
13d SPLIT: dd
15d BORIC: formed by initial letters
17d ADELAIDE: (m)A(n), rev(DIALED), E. Note North American spelling cf. DIALLED
18d KARENINA: rev[A, NINE, RAK(e)]
22d NAVAHO: HAVE A NO spoonerised
24d COWL: CO, W(astefu)L
25d UPON: "across" = UP ON

Virtually all of DA's creativity budget seemed to go into constructing the very demanding grid concept - the clues themselves are pretty uninspired by his standards.